Tracking of phone call according to a displayed telephone-number is known in the art. Some exemplary publications are U.S. Pat. Nos. 7,120,235, 7,505,920, 7,555,106 or International application WO2005/086980.
Some web sites also relate to tracking a phone call, for example, http://paypercall.attinteractive.com/default.aspx, http://avidtrak.com/avidtrak, http://thenextweb.com/2010101/05/google-launching-pay-per-call-mobile-ads.